Frame borders

I have a small problem. I draw my OpenGL - Objects in a Window which is inherit from QGLWidget (a QT - class). My object is for example a cube. If i touch or hit the frame my polygon lines don’t go with the object instead they will bend with the border and the form of the object will be changed. This happens only with some lines not with all.
I’m sure that i have no wrong code. This happens with a simple triangles too. What’s the reason ? Is this a problem from OpenGL oder QT 1.45 ?
Thanks very much

Maybe try to feed glViewport with the correct window size and gluViewport with the correct aspect ratio?